I think you'll find the requirement for a minimum qualification is becoming pretty much the norm for those working with school-age children in any case. Even classroom assistants in many authorities are required to obtain qualifications these days.
I shouldn't think it will be like teaching or nursing in that you have to be qualified before you can get the job. More likely people will be required to train towards NVQ type qualifications as they work.
"Even classroom assistants"!!! - You make us sound like 2nd class citizens!
Yes, you are right, many authorities ask for qualifications; in my current school, applications are only accepted from people with NVQ2 or higher.
However, my question was - will it become compulsory? My friend believes that even people already in-post will be required to qualify. Can't see how this will work myself, and I can't find anything on the internet, so I just wanted clarification.